It could be said that if you don't have those couple of things, as well as a few more, than it isn't love, but only infatuation. That is the part you two may not be getting with this love thing.
That doesn't mean that people that are truly in love don't end up growing apart for several different reasons, because it can, and does, happen.
And, so, by saying that, I will also say there is no such thing as love at first sight. Or, at least in the kind of love for people to form a marriage. That would be an attraction, an infatuation, or something along those lines that could very will grow into love. But, very well could not.
The only love at first sight would be with parents and their children. That love at first sight is real, I promise you that. It is similar to the love you could feel for your significate other, but not exactly the same.
Also, love at first sight could be with things. I mean you may love a plant for example upon seeing it, but you don't have to respect it. All it has to do is look pretty or smell good. But, not the same kind of love either.
There are different kinds of love that you will realize once you have experienced them.
Edit to add: When you feel in your heart that you will surely die for this person to protect them, to keep them safe, then you have truly experienced love for a person.